A fuzzy-logic light attenuation model was developed and validated for a stirred-tank photobioreactor. Based on this model, local light intensities were used to calculate local specific growth rates of the cyanobacteria Synechococcus PCC 7942. The light regime for maximization of biomass space-time yield in a batch process was estimated using a genetic algorithm taking into account the integral average of the individual growth rates. (c) 2006 Wiley Periodicals, Inc.